What are flower and season tiles, and do all sets include them?

Flower tiles depict the four traditional Chinese flowers (Plum, Orchid, Chrysanthemum, Bamboo) and Season tiles depict the four seasons (Spring, Summer, Autumn, Winter). Each bonus tile scores 1 fan and is set aside immediately when drawn, with the player drawing a replacement tile from the back wall. Not all rulesets use them; some competitive formats remove bonus tiles entirely for a cleaner game, but most traditional and social sets include all eight.